Attending his second NATO summit in Brussels this week, President Trump should deliver a stark message to the Belgian government: Increase defense spending now or see NATO headquarters relocated to the British capital.

Such an ultimatum would be absolutely justified. While Belgium has the honor of hosting the alliance that has done more than any other in history to secure freedom and security, it spends next to nothing on defense. The latest NATO figures show that when it comes to the most important measure of contribution to the alliance (defense spending as a percentage of gross domestic product and equipment spending as a percentage of defense budget) Belgium is second-worst in both cases.